This invention relates to a heat exchanger system and particularly, but not exclusively, to a water heating system.
It is difficult to maintain the overall efficiency of a central heating system because of the large variation in demand on the system caused by wide variation of temperature externally of the building being heated and this means that the heating plant must be capable of a very large turndown range. Known boilers which are currently in use all have the disadvantage of a reduction in thermal efficiency as turndown is increased. One method of overcoming this problem is to use a system in which a plurality of boilers are connected in parallel between inflow and outflow conduits, each boiler being connected to a separate flue which leads to a common main flue. The total output of the boilers is sufficient to cater for the maximum demand, and as the demand falls the number of boilers in operation is reduced in order to maintain the desired water temperature. Even with this system the efficiency of the system as a whole is reduced as the number of operating boilers is reduced. The reason for this is that the radiation losses from the boilers remain constant and natural draught draws cold air through the boilers which are not in operation. This has the effect of cooling down the water flowing through the inoperative boilers. Another disadvantage of this known system is that each boiler needs a separate flue and this is expensive and difficult to install.